While traditional shower designs usually include a floor with a raised front edge to contain the spread of water and splatter, this raised edge is not an absolute requirement. Shower basins can be fitted into a floor in such a way that the existing level floor transitions smoothly into a shallow, sloped basin.

The basin is curved enough to ensure efficient collection of water toward the drain, but shallow enough so that stable footing is not compromised. The smooth transition from level floor to sloped basin, unencumbered by any type of a water barrier, produces a sleek and clean appearance. It also eliminates a “trip hazard”.

Showers with smooth, “flush” transitions are also referred to as “barrier free” showers, because they pose no barrier to a person getting in or out of the shower alcove. They are also referred to as “roll-in showers”, because they are naturally accessible to bathers who use wheeled devises, such as walkers or wheelchairs.

While the terms “barrier free” and “roll-in” are descriptive, the smooth transition design is quite appealing in its simple elegance. The lack at the shower entry of a visible, high profile water barrier is a subtle statement that can play together well with accompanying finishes and the overall layout of the bathing area. Even “typical” and “regular” bathrooms gain flair and uniqueness, in an understated way, by eliminating one feature, the water barrier, that is customary and expected in a bathroom.

Installation of Smooth Transition Shower Basins

The walls of a barrier-free shower are created the same way as for regular showers. It is the floor that requires more attention.

If the transition from a level floor to a sloped basin is to be “smooth”, the line where the two portions of the floor meet must end out finishing at the same height. The bottom of the basin, where the water drains, must somehow finish at a lower elevation than anywhere else on the entire bathroom floor.

This cannot be accomplished by raising the elevation of the level floor, because then there would be a major problem where the bathroom floor meets the floor in the rest of the house. As soon as someone opens the bathroom door, they would have to step up a couple of inches onto the higher floor. Also, everything else would be offset: There would be plumbing issues where the toilet and vanity connect; height issues with recessed medicine cabinets and windows; clearance issues with linen closet doors. In general, raising the elevation of the level floor is not an option.

The solution is to lower the floor under the shower floor basin. This can be done by eliminating the floor and subfloor and exposing the floor joists. The joists can then be notched lengthwise so that the cut top of the joists are lower than their uncut neighbors. This provides a lower starting point for rebuilding the shower basin floor, and results in a lower finished surface when the whole thing is complete.

The amount that the joists are cut down is calculated by subtracting the depth of the shower basin from the height of the finished floor. Between 1 ½ “ and 2” is an adequate depth for a shower basin, but less than this needs to be removed from the joists. By blocking and inserting the new subfloor between the joists, usually only a small fraction of an inch needs to be removed from the top of each joist under the shower area.

Joists that have been cut back in this manner can be reinforced by sandwiching them with 1/8” thick steel through-bolted with ¼” bolts. The steel should run the length of the joist, ending on top of supporting structures on either end.

Once the subfloor has been positioned height-wise in relation to the anticipated height of the level floor, the shower basin can be installed. If the shower basin and the level floor are made of dissimilar materials, the joint between them will be made watertight with 100% silicone caulk.

If the shower basin and the level floor are finished with contiguous and newly installed ceramic (or porcelain or stone) tiles, water tightness will be assured by a membrane underlayment. The membrane underlayment is installed as a single sheet under the ceramic tiles. It flows, uninterrupted, across the level floor and into the basin, sealing the transition from water leakage.